From the CW: "Hoping to find a weapon powerful enough to defeat Amara (guest star Emily Swallow), Dean convinces "Castiel," who is still Lucifer, to send him back in time to the last reported sighting of the Hand of God. Lucifer sees the potential in getting his hands on this weapon so goes along as Castiel and sends Dean to 1944 to the fated submarine mission that sunk the Hand of God. Meanwhile, continuing his charade with Sam while they wait for Dean‘s return, Lucifer plans his next move."